Jesus Romero, Mauricio Bellini
Using a recently introduced 5D Riemann flat metric, we investigate the possibility of introducing dissipation in the dynamics of the inflaton field on an effective 4D FRW metric, in the framework of the STM theory of gravity.
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I study the power-law and de Sitter expansions for the universe during inflation from the STM theory of gravity. In a de Sitter expansion the additional dimension is related to the cosmological constant. I find from experimental data that the mass of the inflaton field is $m^2=2/(3Ψ^2)$. In power-law expansion, the fifth coordinate appears to be a dimensionless constant. The interesting here is that the $Ψ$-value depends on the initial conditions. I find the 5D line element for this inflationary expansion, which is a function of the classical component of the inflaton.
It has been suggested that wormholes and other non-trivial geometrical structures might have been formed during the quantum cosmological era ($t\sim 10^{-43}$s). Subsequent inflation of the universe might have enlarged these structures to macroscopic sizes. In this paper, spherical geometrical structures in an inflationary RW background are derived from the Einstein equations, using a constraint on the energy-momentum tensor which is an extension of the one expected for inflation. The possibility of dynamical wormholes and other spherical structures are explored in the framework of the solutio…
We study the geometrical properties of scale-invariant two-field models of inflation. In particular, we show that when the field-derivative space in the Einstein frame is maximally symmetric during inflation, the inflationary predictions can be universal and independent of the details of the theory.
Geometrical scalar back-reaction effects in inflation
本研究从广义相对论拉格朗日表述出发，探究闭合扩展流形几何边界项在冷、温暴胀宇宙中引发的时空波产生，分析了标量、张量模式的演化特征，提出该机制可提供新的宇宙学引力波源。
Geometrical origin of inflation in Weyl-invariant Einstein-Cartan gravity
本文证明了二次Weyl不变Einstein-Cartan引力中内建的标量自由度能驱动暴胀，且预测与观测高度吻合，揭示了暴胀的几何起源。
We derive a Higgs inflationary model in the context of a complex geometrical scalar-tensor theory of gravity. In this model the Higgs inflaton scalar field has geometrical origin playing the role of the Weyl scalar field in the original non-riemannian background geometry. The energy scale enough to generate inflation from the Higgs energy scale is achieved due to the compatibility of the theory with its background complex Weyl-integrable geometry. We found that for a number of e-foldings $N=63$, a nearly scale invariant spectrum for the inflaton is obtained with an spectral index $n_s\simeq 0.…
We study the geometrical instability arising in multi-field models of inflation with negatively-curved field space. We analyse how the homogeneous background evolves in presence of geometrical destabilisation, and show that, in simple models, a kinematical backreaction effect takes place that shuts off the instability. We also follow the evolution of the unstable scalar fluctuations. We show that they assist the kinematical backreaction while remaining in the perturbative regime. We conclude that, in the simplest models of geometrical destabilisation, inflation does not end prematurely, but ra…
We study geometrical destabilization of inflation with the aim of determining the fate of excited unstable modes. We use numerical lattice simulations to track the dynamics of both the inflaton and the spectator field. We find that geometrical destabilization is a short-lived phenomenon and that a negative feedback loop prevents field fluctuations from growing indefinitely. As a result, fields undergoing geometrical destabilization are merely shifted to a new classical configuration corresponding to a uniform value of the spectator field within a Hubble patch.
We investigate cosmological inflationary scenarios from a gravitoelectromagnetic theory. Our work is formulated in the light of a recently introduced geometrical Weyl-Invariant scalar-tensor theory of gravity, where the nature of both the electromagnetic potential and the inflaton field is attributed to the space-time geometry. We obtain a Harrison-Zeldovich power spectrum for quantum fluctuations of the inflaton field. In our model the electromagnetic fields have also a nearly scale invariant power spectrum for a power-law inflation. We found that the the seed magnetic fields have a nearly sc…
We show the existence of a general mechanism by which heavy scalar fields can be destabilized during inflation, relying on the fact that the curvature of the field space manifold can dominate the stabilizing force from the potential and destabilize inflationary trajectories. We describe a simple and rather universal setup in which higher-order operators suppressed by a large energy scale trigger this instability. This phenomenon can prematurely end inflation, thereby leading to important observational consequences and sometimes excluding models that would otherwise perfectly fit the data. More…
We study the motion of a BPS D3-brane in the NS5-brane ring background. The radion field becomes tachyonic in this geometrical set up. We investigate the potential of this geometrical tachyon in the cosmological scenario for inflation as well as dark energy. We evaluate the spectra of scalar and tensor perturbations generated during tachyon inflation and show that this model is compatible with recent observations of Cosmic Microwave Background (CMB) due to an extra freedom of the number of NS5-branes. It is not possible to explain the origin of both inflation and dark energy by using a single …
In this letter we investigate gauge invariant scalar fluctuations of the metric in a non-perturbative formalism for a Higgs inflationary model recently introduced in the framework of a geometrical scalar-tensor theory of gravity. In this scenario the Higgs inflaton field has its origin in the Weyl scalar field of the background geometry. We found a nearly scale invariance of the power spectrum for linear scalar fluctuations of the metric. For certain parameters of the model we obtain values for the scalar spectral index $n_s$ and the scalar to tensor ratio $r$ that fit well with the Planck 201…
Using ideas of STM theory, but starting from a 6D vacuum state, we propose an inflationary model where the universe emerges from the blast of a white hole. Under this approach, the expansion is affected by a geometrical deformation induced by the gravitational attraction of the hole, which should be responsible for the k_{R}-non invariant spectrum of galaxies (and likewise of the matter density) today observed.
The nature of the scalar field responsible for the cosmological inflation, the \qo{inflaton}, is found to be rooted in the most fundamental concept of the Weyl's differential geometry: the parallel displacement of vectors in curved space-time. The Euler-Lagrange theory based on a scalar-tensor Weyl-Dirac Lagrangian leads straightforwardly to the Einstein equation admitting as a source the characteristic energy-momentum tensor of the inflaton field. Within the dynamics of the inflation, e.g. in the slow roll transition from a \qo{false} toward a \qo{true vacuum}, the inflaton's geometry implies…
Gravitational waves during Higgs inflation from complex geometrical scalar-tensor theory of gravity
本研究在复几何标量-张量引力理论下探究希格斯暴胀末期的度规张量涨落，考虑希格斯场相关真空项的额外贡献与对称群修正的非正则函数对标度的影响，得到符合PLANCK 2018结果的近标度不变谱和标量张量比。
We study the dynamics of scalar metric fluctuations in a non-perturbative variational formalism recently introduced, by which the dynamics of an geometrical scalar field $θ$, describes the quantum geometrical effects on a Weylian-like manifold with respect to a background Riemannian space-time. In this letter we have examined an example in the framework of inflationary cosmology. The resulting spectral predictions are in very good agreement with observations and other models of inflation.
In a modest attempt to present potentially new paradigms in Cosmology, including its inflationary epoch, and initiate discussions, I review in this article some novel, string-inspired cosmological models, which entail a purely geometrical origin of the Dark sector of the Universe but also of its observed matter-antimatter asymmetry. The models contain gravitational (string-model independent, Kalb-Ramond (KR)) axion fields coupled to primordial gravitational anomalies via CP-violating interactions. The anomaly terms are four-space-time-dimensional remnants of the Green-Schwarz counterterms appe…
A formalization of the recently introduced formalism for inflation is developed from noncompact Kaluza-Klein theory. In particular, the case for a single scalar field inflationary model is studied. We obtain that the scalar potential, which assume different representations in different frames, has a geometrical origin.
We investigate gauge invariant scalar fluctuations of the metric during inflation in a non-perturbative formalism in the framework of a recently introduced scalar-tensor theory of gravity formulated on a Weyl-Integrable geometry. We found that the Weyl scalar field can play the role of the inflaton field in this theory. As an application we study the case of a power law inflation. In this case the quasi-scale invariance of the spectrum for scalar fluctuations of the metric is achieved for determined values of the $ω$ parameter of the scalar-tensor theory. In our formalism the physical inflaton…
We outline the key-steps towards the construction of a physical, fully relativistic cosmology, in which we aim to trace Dark Energy and Dark Matter back to physical properties of space. The influence of inhomogeneities on the effective evolution history of the Universe is encoded in backreaction terms and expressed through spatially averaged geometrical invariants. These are absent and interpreted as missing dark fundamental sources in the standard model. In the inhomogeneous case they can be interpreted as energies of an emerging scalar field (the morphon). These averaged invariants vanish fo…
Power law coupling Higgs-Palatini inflation with a congruence between physical and geometrical symmetries
本文研究了幂律耦合 Higgs-Palatini 暴胀模型，通过施加物理与几何对称性的一致性条件，在强耦合极限下导出了标量-张量型不变作用量，并获得了符合观测数据的标度不变功率谱与张量标量比。
We study gravitational waves generated during the inflationary epoch in presence of a decaying cosmological parameter on a 5D geometrical background which is Riemann flat. Two examples are considered, one with a constant cosmological parameter and the second with a decreasing one.
Torsion is a geometrical object, required by quantum mechanics in curved spacetime, which may naturally solve fundamental problems of general theory of relativity and cosmology. The black-hole cosmology, resulting from torsion, could be a scenario uniting the ideas of the big bounce and inflation, which were the subject of a recent debate of renowned cosmologists.
We study the variational principle on a Hilbert-Einstein action in an extended geometry with torsion taking into account non-trivial boundary conditions. We obtain an effective energy-momentum tensor that has its source in the torsion, which represents the matter geometrically induced. We explore about the existence of magnetic monopoles and gravitational waves in this torsional geometry. We conclude that the boundary terms can be identified as possible sources for the cosmological constant and torsion as the source of magnetic monopoles. We examine an example in which gravitational waves are …
We study the origin of the universe (or pre-inflation) by suggesting that the primordial space-time in the universe suffered a global topological phase transition, from a 4D Euclidean manifold to an asymptotic 4D hyperbolic one. We introduce a complex time, $τ$, such that its real part becomes dominant after started the topological phase transition. Before the big bang, $τ$ is a space-like coordinate, so that can be considered as a reversal variable. After the phase transition is converted in a causal variable. The formalism solves in a natural manner the quantum to classical transition of the…
In loop quantum gravity, modifications to the geometrical density cause a self-interacting scalar field to accelerate away from a minimum of its potential. In principle, this mechanism can generate the conditions that subsequently lead to slow-roll inflation. The consequences for this mechanism of various quantization ambiguities arising within loop quantum cosmology are considered. For the case of a quadratic potential, it is found that some quantization procedures are more likely to generate a phase of slow--roll inflation. In general, however, loop quantum cosmology is robust to ambiguities…
Rigorous derivation of dark energy and inflation as geometry effects in Covariant Canonical Gauge Gravity
本文从协变正则规范引力理论出发，通过引入二次Riemann-Cartan项和挠率，将宇宙学常数推广为时间函数并导出暗辐射型几何修正，得到与ΛCDM兼容且能描述反弹、大爆炸及晚期暗能量演化的宇宙学模型，并用低红移观测验证了该理论的可行性。
In this work we study slow-roll inflation for a vector-tensor model with massive vector fields non-minimally coupled to gravity. The model under consideration has arbitrary parameters for each geometrical coupling. Taking into account a spatially flat FRW type universe and a general vector fields (with temporal and spatial components), we get the general expressions for equation of motion and the total energy momentum tensor. In this scenario, the isotropy of expansion is guaranteed considering a triplet of orthogonal vector fields, but the effective mass of the vector field is of the order of…
We study the cosmological inflation within the context of f(Q, T) gravity, wherein Q is the nonmetricity scalar and T is the trace of the matter energy-momentum tensor. By choosing a linear combination of Q and T, we first analyze the realization of an inflationary scenario driven via the geometrical effects of the linear f(Q, T) gravity and then, we obtain the modified slow-roll parameters, the scalar and the tensor spectral indices, and the tensor-to-scalar ratio for the proposed model. In addition, by choosing three inflationary potentials, i.e. the power-law, hyperbolic and natural potenti…
We present an analytic, perturbative solution to the Einstein equations with a scalar field that describes dynamical black holes in a slow-roll inflationary cosmology. We show that the metric evolves quasi-statically through a sequence of Schwarzschild-de Sitter like metrics with time dependent cosmological constant and mass parameters, such that the cosmological constant is instantaneously equal to the value of the scalar potential. The areas of the black hole and cosmological horizons each increase in time as the effective cosmological constant decreases, and the fractional area increase is …
Independent connection in ACTion during inflation
本文基于ACT的最新观测约束，提出与度规无关的动力学仿射联络分量可驱动暴胀，在最小模型中给出相关宇宙学参数预测，证明存在暴胀吸引子，并讨论了希格斯玻色子的作用。
We apply the full set of most update dynamical and geometrical data in cosmology to the nonextensive Barrow entropic holographic dark energy. We show that the data point towards an extensive Gibbs-like entropic behaviour for the cosmological horizons, which is the extreme case of the Barrow entropy, with the entropy parameter being $Δ> 0.86$, close to the maximum threshold of $Δ=1$ where the fractal dimension of the area-horizon becomes almost or just the volume and the intensivity is recovered. Futhermore, we find that the standard Bekenstein area-entropy limit ($Δ= 0$) is excluded by the set…
Space-time-matter gravity as the origin of rotation in 4-D stationary and axisymmetric vacuum solutions
研究提出时空物质（STM）理论，将4D稳态轴对称真空解中的旋转解释为5D流形额外维度的诱导效应，为暗物质相关的观测修正提供新解释。
Matrix models of Yang-Mills type lead to an emergent gravity theory, which may not require fine-tuning of a cosmological constant. We find cosmological solutions of Friedmann-Robertson-Walker type. They generically have a big bounce, and an early inflation-like phase with graceful exit. The mechanism is purely geometrical, no ad-hoc scalar fields are introduced. The solutions are stabilized through vacuum fluctuations and are thus compatible with quantum mechanics. This leads to a Milne-like universe after inflation, which appears to be in remarkably good agreement with observation and may pro…
Inflation in Myrzakulov $F(R,T)$ Gravity: A Comparative Study in Metric, Symmetric Teleparallel, and Weitzenböck Formalisms
本文在 Myrzakulov Gravity 框架下统一研究了度规、遥平行和对称遥平行三种形式中的宇宙暴胀，并扩展至包含曲率与挠率的 $F(R,T)$ 混合模型，推导暴胀动力学及可观测物理量，证明其能灵活匹配观测约束并产生可区分的暴胀特征。
In this paper we discuss a spacetime having the topology of S^3 x R but with a different smoothness structure leading to a geometric model for inflation, called geometric inflation. In particular this spacetime is not globally hyperbolic and we obtain a time line with a spatial topology change from the 3-sphere to a homology 3-sphere and back. The topology of the spacetime remains invariant. Among the infinite possible smoothness structures of this spacetime, we choose a homology 3-sphere constructed from the knot 8_{10} with hyperbolic geometry, i.e. admitting a homogenous metric of negative …
We investigate some cosmological models arising from a non-minimal coupling of a fermionic field to gravity in the geometrical setting of Einstein-Cartan-Sciama-Kibble gravity. The role played by the non-minimal coupling together with torsion in facing problems such as cosmological singularity, inflation and dark energy is discussed.
Dark energy and inflation invoked in CCGG by locally contorted space-time
本文研究 CCGG 的宇宙学后果，利用挠率、扭率标量场和二次尺度不变引力修正，在单一形变参数下得到三类可通向暗能量时代的宇宙，并由 SNeIa 等观测约束该理论。
The question of whether Cosmic Microwave Background (CMB) temperature and polarization data from Planck favor a spatially closed Universe with curvature parameter $Ω_K<0$ has been the subject of recent intense discussions. Attempts to break the geometrical degeneracy combining Planck data with external datasets such as Baryon Acoustic Oscillation (BAO) measurements all point towards a spatially flat Universe, at the cost of significant tensions with Planck, which make the resulting dataset combination problematic. Settling this issue requires identifying a dataset which can break the geometric…
Modified gravity: a unified approach to metric-affine models
本文以 Einstein 的 Gamma 平方作用量为基础，采用 Palatini 方法统一构建含挠率与非度量性的度量-仿射修正引力理论，给出传播挠率条件及无需物质源的几何暴胀宇宙学解。
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